happypappy

My Feedback: (10)

Is there an alternative to a bladder tank using 3 lines and a check valve in the exhaust pressure line? How do you set it up and can you set the engine RPM at peak and leave it there with this set up? Thanks!

YUKONFLYR

The bladder tank keeps air out of the fuel by never allowing the two to touch. Using a check valve will keep tank pressure up, however there is still air in the tank and the posibility of foaming fuel allowing the engine to go lean. One bubble or lots of little ones spell disaster for your expensive engine if the fuel foams.

garys

The box that the Tetra tanks come in shows a 3-line setup, but I've never heard of anybody using it in a racing application. I've also never heard of any racers using a check valve in the muffler pressure line, and wouldn't recommend setting any engine at peak RPMs, although in some cases you can get close to it, depending on engine, ect.

rmenke

My Feedback: (13)

Happypappy:

Sort of sounds like you are working with a YS engine? Have never used or sean a bladder tank setup used with 3 lines. Guess you could add another line inside the bladder to use as a sucker or vent line to help get rid of bubbles, but the approach not used in my experience. A additional line increases the odds of something going wrong by 33%. Enough happens to simple designs without adding unnecessary complications. Note that the Jett bladder tanks only have two lines. ENJOY

happypappy

My Feedback: (10)

Should have explained myself a little better I guess. The plane is a club 40 plane with a simple ST GS-40 on it. I had heard about using a tank with the normal clunk in it then adding an additional clunk on the line that supplies pressure. The third line is simply a vent line while filling and gets closed off. The pressure line has a check valve in it to keep a constant pressure in the tank. By keeping the pressure line clunk submerged the pressure should never change as the tank level lowers as only what is being used is being replaced at a constant pressure. Anyone know anything about this set up? Obviously the advantage here is, if it is possible, to tune the engine to peak instead of 3-400RPM down and wait for the tank level to drop to lean the engine.

HighPlains

My Feedback: (1)

Actually no, all things being equal. Increasing the number of lines from two to three lowers reliability by 50%.

Assume a MTBF for single line to be 100 hours. With two lines the reliability drops to 50 hours, while adding a third line drops the MTBF to 33.3 hours.

Where MTBF gets interesting (and they pay you the big bucks) is when you do it for electronic systems.

Duane-RCU

My Feedback: (5)

The first Tettra tank I used had three lines. I used my electric fuel pump to fill it. I could cycle the pump and get all the air out, once full I didn't want to just run the pump, in case it put too much pressure on the bladder. Other racers won't notice you are using one, since you won't fill it with a syringe. The system worked fine, I filled it several times on the bench to make sure it worked before putting it in the plane.

djlyon

You are talking about a uniflow system. Common on aerobatic planes. The check valve really doesn't do much for you in your situation. No purpose in a discussion here on gas and liquid flow rates. Setting the rpm 3 to 400 rpm low for this kind of airplane is not primarily to accommodate the pressure head change as the fuel level goes down but rather to accommodate the fuel demand as the prop unloads as the plane gets up to speed. The ground rpm for each engine is going to depend on the fuel demand of that specific engine as it unloads assuming all else in the fuel system is correct.

and Highplains after all the MTBF calculations it's really all about controlling junction temps. Lord I'm glad I'm retired.

HighPlains

My Feedback: (1)

I don't miss semi-log graphs either.

happypappy

My Feedback: (10)

Djlyon - thanks for the corrrect terminology. The check valve should keep fuel fom running out of the tank and through the exhaust when I throttle down since the pressure clunk is now submerged. Remember that in this plane the engine will be run at WOT from the time it leaves the ground. Do you think I can set the needle leaner with this set up than with a standard two line tank? RPMs is speed after all !

daven

My Feedback: (1)

You can set them leaner than you could a conventional tank, but you can't set them to full bore lean. Well you can, but they don't last too long that way.

Better to leave the motor a little room to unload.

Ed Smith

I keep hearing reference to a check valce in the pressure line. IF this is a one way valve then do not do it. because there is no escape route it will create a very high pressure build up in the tank and flood the engine. Normal muffler pressure goes so high then escapes out of the muffler outlet. It is similar to crankcase pressure. It is almost impossible to get an engine to idle using crankcase pressure that pulsates and has no escape route

Ed S.

happypappy

My Feedback: (10)

Actually, it looks like I can run the check valve as the pressure differential would remain the same and all I have to do is tune for it vs the conventional tank. The check valve would be there simply to keep fuel from rushing back up the pressure line when backing off the throttle. Take a look at this pretty simple explanation I found while researching this.
http://www.fraserker.com/heli/uniflo...flow_works.htm

Ed Smith

You are not listening. fuel cannot run up the pressure line when muffler pressure is present, at idle or full throttle. When you are given sound advice, listen to it.

Ed S

gunfighter

My Feedback: (1)

This "Uniflow" guy is all wet! That system would work fine to keep a header tank full for helicopters etc. but would flood a standard engine if the throttle is even slightly reduced.

Try this...with the system he (and you) are talking about. fill the tank, put your finger over the muffler outlet and flip the prop several times. Fuel will start running out the fuel line with ever increasing volume until the fuel is gone or the pressure is reduced / vented. Pressure built up inside the tank has no where to exit. therefore, it will continue to increase as the engine is run.

Now do the same with a bubble less (or a good standard clunk) tank. Fuel will come out in "spurts as the muffler puts pressure on the fuel. Then the flow will stop as the pressure is equalized.

You could NOT set the needle any leaner and expect it to last for an entire tank. With a check valve as you describe it, (and YES, I have tried them) the pressure keeps increasing in the fuel tank until the engine floods.

Just spend the $15.00 and get a Jet or Tetra bubbel less tank and your problem will be solved with out further experimentation.[8D]

happypappy

My Feedback: (10)

Well guys.......I tried it. Put the engine on a stand first after setting up a uniflow tank and ran it with and without the check valve in the muffler. When you back off the fuel does come up into the muffler and out the exhaust. Installed the check valve and ran it again and no more fuel in the exhaust. All I had to do was re-adjust the HS needle for the constant pressure. When I backed off the engine it did run a little rich but cleaned up pretty quick and I could bring it back to an idle as well. I never had to re-adjust the idle at all. I put the engine back in the plane, with a uniflow set up and the check valve and flew it several times today at two clicks off peak and it ran like a champ all day. What has to be remembered here is that this engine never has to come off of WOT from the time it leaves the ground unlike other types of flying. That makes this set up pretty nice.

luv to race

My Feedback: (1)

I tried to read this thread, I''m lost. What''s are you trying to achieve? Check valve? Does this keep pressure from escaping from the tank through the pressure line once it''s built up? Is that what your worried about? I always figured that if the engine was running, you had pressure.

Chris Callow (World Champion, 3 times) uses 3 lines in his Tettra bladder tanks, and no check valve. Seems to work okay for him. But yes, you have to plug the 3rd line (internal bladder vent line) after you fill up. No big deal. The American guys just use 2 lines as Ed and others described.

But it sounds like you trying to get the motor to run on peak at launch, which none of the pylon racers do. There''s nothing to gain by doing this. If I launch 1000 down from peak with minimal constant tank pressure, and it runs perfect. And you launch on peak with tons of tank pressure, and it runs perfect. There''s no gain. But the minute that check valve thing fails, you''ll wish you didn''t have that in the line. That''s just a waste of time.

I live in Apopka Florida, which is close to you Happy.. If you want to come flying with me some day at RCACF, send me a PM. I''d be my pleasure to show you the proven method that every pylon racer uses.

RB

Jim Duda

Perhaps Happy doesn't have a syringe to fuel/de-fuel a two line system...??? If not, then the 3 line system Randy described above used by Chris might be the best solution for him. I also suggest not using a check valve in the system.

jimd

happypappy

My Feedback: (10)

Sorry, have been gone for a while. Yes, I am trying to run the engine at or near peak from start to finish and this system with its balance of pressures seems to do just that. Have run the engine with a single click off peak from start to finish with no issues so far. As far as the check valve longevity goes......YS engines seem to depend on them and thats not such a bad thing.

nik112233

Jim,
Where can I get the pictured bladder tank? What sizes are available?

Thanks,
Nik

luv to race

My Feedback: (1)

http://pspec.com/

vertical grimmace

My Feedback: (1)

Happyhappy, a uniflow plumbed tank is a good alternative for what you want to do.

daven

My Feedback: (1)

Nik,

Additional sizes can also be found at central hobbies. They advertise in many of the mags.

Fxrs_tim

If the Tettra's don't fit your application, Jett makes bladder tanks in different shapes than Tettra. Click on the accessories button.

http://www.jettengineering.com/

combatpigg

My Feedback: (3)

The higher the pressure that there is in the system, the closer to peak you can launch at provided that the fuel is routed through a vacuum actuated check valve [regulator]. Similar to timed fuel injection. The engine is fed a metered shot of fuel every time the regulator sees a negative pulse from the crankcase. This is how fast combat engines could get flawless runs over and over inspite of the G forces. Some local racers tried this system in the F1 days and liked it. IIRC a National record was held for awhile with such an equipped plane.
In recent years the Nelson engines have been engineered to be immune enough to fuel delivery problems running straight off the tank that regulators became uneccessary.